6.1 Engineering Controls
Engineering controls, personal protective equipment, hygiene practices, and administrative controls each play a role in a comprehensive laboratory safety program. Implementation of specific measures must be carried out on a case-by-case basis, using the following criteria for guidance in making decisions. Assistance is available from UHS.
A. Fume Hoods
The laboratory fume hood is the major protective device available to laboratory workers. It is designed to capture chemicals that escape from their containers or apparatus and to remove them from the laboratory environment before they can be inhaled. Characteristics to be considered in requiring fume hood use are physical state, volatility, toxicity, flammability, eye and skin irritation, odor, and the potential for producing aerosols.
A fume hood should be used if a proposed chemical procedure exhibits any one of the following characteristics:
- Airborne concentrations might approach the action level (or permissible exposure limit)
- Flammable vapors might approach one tenth of the lower explosion limit
- Materials of unknown toxicity are used or generated
- The odor produced is annoying to laboratory occupants or adjacent units
Do NOT use a fume hood for the following:
- For use with biohazardous materials
- For waste disposal. It is a violation of environmental regulations to intentionally send waste up the fume hood stack
- For storing materials. Keep only the materials necessary for the experiment inside of the fume hood, excess materials increase the potential severity of incidents and reduce effectiveness of ventilation. Toxic, corrosive or odiferous materials should be stored in ventilated cabinets if ventilation is desired while in storage.
- With electrical receptacles such as power strips. Electrical receptacles are spark and ignition sources, and are not permitted for use inside the fume hood
The use of ductless fume cabinets is NOT permitted at the University of Minnesota
Procedures that can generally be carried out safely outside the fume hood include those involving the following:
- Water-based solutions of salts, dilute acids, bases, or other reagents
- Very low volatility liquids or solids
- Closed systems that do not allow significant escape to the laboratory environment
- Extremely small quantities of otherwise problematic chemicals. The procedure itself must be evaluated for its potential to increase volatility or produce aerosols.
In specialized cases, fume hoods will contain exhaust treatment devices, such as water wash-down for perchloric acid use, or charcoal or HEPA filters for removal of particularly toxic or radioactive materials. Fume hoods must not be used for work with infectious agents.
Fume hoods must be monitored daily by the user to ensure that air is moving into the hood. Any malfunctions must be reported immediately to Facilities Management (612-624-2900). The fume hood should have a continuous reading device, such as a pressure gauge, to indicate that air is moving correctly. Users of older fume hoods without continuous reading devices should attach a strip of tissue, kim wipe or light string to the bottom of the vertical sliding sash. The user must ensure the fume hood and baffles are not blocked by equipment and bottles, as air velocity through the face may be decreased. UHS staff will measure the average face velocity of each fume hood annually with a velometer or a thermo-anemometer.
Acceptable Operating Range
The acceptable operating range for standard fume hoods is 80 to 120 linear feet per minute (64-96 fpm for low flow hoods), at the designated sash opening – usually 18 inches for a vertically-sliding sash and 30 inches for a horizontally-sliding sash. If, during the annual check, a fume hood is operating outside of this range, UHS staff may request that you check to ensure that the exhaust slots are not blocked by bottles and equipment. If a fume hood is not working properly, please contact Facilities Management at 612-624-2900 to schedule a repair.
Fume hoods are tested for acceptable operating range annually by UHS. A sticker will be placed on the fume hood indicating the range at which the hood is operating and it will be signed and dated. If a fume hood does not have a current certification sticker (dated within the past year), call UHS at 612-626-6002 to schedule a test.
During maintenance of fume hoods, laboratories must clean out and if necessary, decontaminate the fume hood and restrict use of chemicals to ensure the safety of maintenance personnel.
C. Safety Shields
Safety shields, such as the sliding sash of a fume hood or a weighted shield that is rated to contain an explosion, are appropriate when working with highly concentrated acids, bases, oxidizers or reducing agents, all of which have the potential for causing sudden spattering or even explosive release of material. Reactions carried out at non-ambient pressures (vacuum or high pressure) also require safety shields, as do reactions that are carried out for the first time or are significantly scaled up from normal operating conditions.
D. Other Containment Devices
Other containment devices, such as glove boxes or vented gas cabinets, may be required when it is necessary to provide an inert atmosphere for the chemical procedure taking place, when capture of any chemical emission is desirable, or when the standard laboratory fume hood does not provide adequate assurance that overexposure to a hazardous chemical will not occur. The presence of biological or radioactive materials may also mandate certain special containment devices.
Highly localized exhaust ventilation, such as is usually installed over atomic absorption units, may be required for instrumentation that exhausts toxic or irritating materials to the laboratory environment.
Ventilated chemical storage cabinets or rooms should be used when the chemicals in storage have the following hazard characteristics: toxic inhalation hazards, high vapor pressures/volatile materials, strong odors, or corrosive vapors.